net.sf.saxon.expr

## Class CardinalityChecker

- java.lang.Object
- - net.sf.saxon.expr.Expression
  - - net.sf.saxon.expr.UnaryExpression
    - - net.sf.saxon.expr.CardinalityChecker

- All Implemented Interfaces:
    Serializable, SourceLocator, LocationProvider, SaxonLocator, InstructionInfo, Locator

      public final class CardinalityChecker
      extends UnaryExpression

  A CardinalityChecker implements the cardinality checking of "treat as": that is, it returns the supplied sequence, checking that its cardinality is correct
  See Also:
    Serialized Form

- - ### Field Summary

    - ### Fields inherited from class net.sf.saxon.expr.UnaryExpression

      `operand`

    - ### Fields inherited from class net.sf.saxon.expr.Expression

      `EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, INHERITED_CONTEXT, INSPECTION_CONTEXT, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, NAVIGATION_CONTEXT, NODE_VALUE_CONTEXT, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, W3C_CONSUMING, W3C_FREE_RANGING, W3C_GROUP_CONSUMING, W3C_MOTIONLESS, WATCH_METHOD`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `int` | `computeCardinality()` Determine the static cardinality of the expression
    `int` | `computeSpecialProperties()` Get the static properties of this expression (other than its type).
    `Expression` | `copy()` Copy an expression.
    `static String` | `depictSequenceStart(SequenceIterator seq, int max)` Show the first couple of items in a sequence in an error message
    `boolean` | `equals(Object other)` Is this expression the same as another expression?
    `Item` | `evaluateItem(XPathContext context)` Evaluate as an Item.
    `void` | `explain(ExpressionPresenter out)` Diagnostic print of expression structure.
    `ExpressionCompiler` | `getExpressionCompiler()` Return the compiler of the CardinalityCheck expression
    `String` | `getExpressionName()` Get a name identifying the kind of expression, in terms meaningful to a user.
    `int` | `getImplementationMethod()` An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
    `IntegerValue[]` | `getIntegerBounds()` For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis.
    `ItemType` | `getItemType(TypeHierarchy th)` Determine the data type of the items returned by the expression, if possible
    `int` | `getRequiredCardinality()` Get the required cardinality
    `RoleLocator` | `getRoleLocator()` Get the RoleLocator, which contains diagnostic information for use if the cardinality check fails
    `int` | `getStreamability(int syntacticContext, boolean allowExtensions, List<String> reasons)` Get the "sweep" of this expression as defined in the W3C streamability specifications.
    `CardinalityCheckerAdjunct` | `getStreamingAdjunct()` Get a class that supports streamed evaluation of this expression
    `int` | `hashCode()` get HashCode for comparing two expressions.
    `SequenceIterator` | `iterate(XPathContext context)` Iterate over the sequence of values
    `static Expression` | `makeCardinalityChecker(Expression sequence, int cardinality, RoleLocator role)` Factory method to construct a CardinalityChecker.
    `Expression` | `optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType)` Perform optimisation of an expression and its subexpressions.
    `void` | `process(XPathContext context)` Process the instruction, without returning any tail calls
    `void` | `setErrorCode(String code)` Set the error code to be returned (this is used when evaluating the functions such as exactly-one() which have their own error codes)
    `String` | `toString()` The toString() method for an expression attempts to give a representation of the expression in an XPath-like form.
    `Expression` | `typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType)` Type-check the expression

    - ### Methods inherited from class net.sf.saxon.expr.UnaryExpression

      `displayOperator, getBaseExpression, iterateSubExpressions, promote, replaceSubExpression, simplify`

    - ### Methods inherited from class net.sf.saxon.expr.Expression

      `addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getEvaluationMethod, getExecutable, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasVariableBinding, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterateEvents, iterateSubExpressionInfo, markTailFunctionCalls, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, toPattern, toStreamingPattern, typeError`

    - ### Methods inherited from class java.lang.Object

      `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

- - ### Method Detail

    - #### makeCardinalityChecker

          public static Expression makeCardinalityChecker(Expression sequence,
                                          int cardinality,
                                          RoleLocator role)

      Factory method to construct a CardinalityChecker. The method may create an expression that combines the cardinality checking with the functionality of the underlying expression class
      Parameters:
        `sequence` - the base sequence whose cardinality is to be checked
        `cardinality` - the required cardinality
        `role` - information to be used in error reporting
      Returns:
        a new Expression that does the CardinalityChecking (not necessarily a CardinalityChecker)

    - #### getRequiredCardinality

          public int getRequiredCardinality()

      Get the required cardinality
      Returns:
        the cardinality required by this checker

    - #### typeCheck

          public Expression typeCheck(ExpressionVisitor visitor,
                             ExpressionVisitor.ContextItemType contextItemType)
                               throws XPathException

      Type-check the expression
      Overrides:
        `typeCheck` in class `UnaryExpression`
      Parameters:
        `visitor` - an expression visitor
        `contextItemType` - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to `Type.ITEM_TYPE`
      Returns:
        the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
      Throws:
        `XPathException` - if an error is discovered during this phase (typically a type error)

    - #### optimize

          public Expression optimize(ExpressionVisitor visitor,
                            ExpressionVisitor.ContextItemType contextItemType)
                              throws XPathException

      Perform optimisation of an expression and its subexpressions.

      This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.

      Overrides:
        `optimize` in class `UnaryExpression`
      Parameters:
        `visitor` - an expression visitor
        `contextItemType` - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to `Type.ITEM_TYPE`
      Returns:
        the original expression, rewritten if appropriate to optimize execution
      Throws:
        `XPathException` - if an error is discovered during this phase (typically a type error)

    - #### setErrorCode

          public void setErrorCode(String code)

      Set the error code to be returned (this is used when evaluating the functions such as exactly-one() which have their own error codes)
      Parameters:
        `code` - the error code to be used

    - #### getRoleLocator

          public RoleLocator getRoleLocator()

      Get the RoleLocator, which contains diagnostic information for use if the cardinality check fails
      Returns:
        the diagnostic information

    - #### getImplementationMethod

          public int getImplementationMethod()

      An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided. This implementation provides both iterate() and process() methods natively.
      Overrides:
        `getImplementationMethod` in class `Expression`
      Returns:
        the implementation method, for example `Expression.ITERATE_METHOD` or `Expression.EVALUATE_METHOD` or `Expression.PROCESS_METHOD`

    - #### getStreamability

          public int getStreamability(int syntacticContext,
                             boolean allowExtensions,
                             List<String> reasons)

      Get the "sweep" of this expression as defined in the W3C streamability specifications. This provides an assessment of stylesheet code against the W3C criteria for guaranteed streamability, and is implemented to allow these criteria to be tested. It is not the case that all expression that emerge as streamable from this analysis are currently capable of being streamed by Saxon
      Overrides:
        `getStreamability` in class `Expression`
      Parameters:
        `syntacticContext` - one of the values `Expression.NAVIGATION_CONTEXT`, `Expression.NODE_VALUE_CONTEXT`, `Expression.INHERITED_CONTEXT`, `Expression.INSPECTION_CONTEXT`
        `allowExtensions` - if false, the definition of "guaranteed streamability" in the W3C specification is used. If true, Saxon extensions are permitted, which make some
        `reasons` - the caller may supply a list, in which case the implementation may add to this list a message explaining why the construct is not streamable, suitable for inclusion in an error message.
      Returns:
        one of the values `Expression.W3C_MOTIONLESS`, `Expression.W3C_CONSUMING`, `Expression.W3C_GROUP_CONSUMING`, `Expression.W3C_FREE_RANGING`

    - #### getStreamingAdjunct

          public CardinalityCheckerAdjunct getStreamingAdjunct()

      Get a class that supports streamed evaluation of this expression
      Overrides:
        `getStreamingAdjunct` in class `Expression`
      Returns:
        the relevant StreamingAdjunct, or null if none is available

    - #### getIntegerBounds

          public IntegerValue[] getIntegerBounds()

      For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis. The default implementation returns null, meaning "unknown" or "not applicable". Other implementations return an array of two IntegerValue objects, representing the lower and upper bounds respectively. The values UNBOUNDED_LOWER and UNBOUNDED_UPPER are used by convention to indicate that the value may be arbitrarily large. The values MAX_STRING_LENGTH and MAX_SEQUENCE_LENGTH are used to indicate values limited by the size of a string or the size of a sequence.
      Overrides:
        `getIntegerBounds` in class `Expression`
      Returns:
        the lower and upper bounds of integer values in the result, or null to indicate unknown or not applicable.

    - #### iterate

          public SequenceIterator iterate(XPathContext context)
                                   throws XPathException

      Iterate over the sequence of values
      Overrides:
        `iterate` in class `Expression`
      Parameters:
        `context` - supplies the context for evaluation
      Returns:
        a SequenceIterator that can be used to iterate over the result of the expression
      Throws:
        `XPathException` - if any dynamic error occurs evaluating the expression

    - #### depictSequenceStart

          public static String depictSequenceStart(SequenceIterator seq,
                                   int max)

      Show the first couple of items in a sequence in an error message
      Parameters:
        `seq` - iterator over the sequence
        `max` - maximum number of items to be shown
      Returns:
        a message display of the contents of the sequence

    - #### evaluateItem

          public Item evaluateItem(XPathContext context)
                            throws XPathException

      Evaluate as an Item. For this class, this implies checking that the underlying expression delivers a singleton.
      Overrides:
        `evaluateItem` in class `Expression`
      Parameters:
        `context` - The context in which the expression is to be evaluated
      Returns:
        the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
      Throws:
        `XPathException` - if any dynamic error occurs evaluating the expression

    - #### process

          public void process(XPathContext context)
                       throws XPathException

      Process the instruction, without returning any tail calls
      Overrides:
        `process` in class `Expression`
      Parameters:
        `context` - The dynamic context, giving access to the current node, the current variables, etc.
      Throws:
        `XPathException` - if a dynamic error occurs

    - #### getItemType

          public ItemType getItemType(TypeHierarchy th)

      Determine the data type of the items returned by the expression, if possible
      Overrides:
        `getItemType` in class `UnaryExpression`
      Parameters:
        `th` - the type hierarchy cache
      Returns:
        a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known in advance)

    - #### computeCardinality

          public int computeCardinality()

      Determine the static cardinality of the expression
      Overrides:
        `computeCardinality` in class `UnaryExpression`
      Returns:
        the computed cardinality, as one of the values `StaticProperty.ALLOWS_ZERO_OR_ONE`, `StaticProperty.EXACTLY_ONE`, `StaticProperty.ALLOWS_ONE_OR_MORE`, `StaticProperty.ALLOWS_ZERO_OR_MORE`

    - #### computeSpecialProperties

          public int computeSpecialProperties()

      Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.
      Overrides:
        `computeSpecialProperties` in class `UnaryExpression`
      Returns:
        the special properties, as a bit-significant integer

    - #### copy

          public Expression copy()

      Copy an expression. This makes a deep copy.
      Specified by:
        `copy` in class `Expression`
      Returns:
        the copy of the original expression

    - #### equals

          public boolean equals(Object other)

      Is this expression the same as another expression?
      Overrides:
        `equals` in class `UnaryExpression`

    - #### hashCode

          public int hashCode()

      get HashCode for comparing two expressions. Note that this hashcode gives the same result for (A op B) and for (B op A), whether or not the operator is commutative.
      Overrides:
        `hashCode` in class `UnaryExpression`

    - #### getExpressionCompiler

          public ExpressionCompiler getExpressionCompiler()

      Return the compiler of the CardinalityCheck expression
      Overrides:
        `getExpressionCompiler` in class `Expression`
      Returns:
        the relevant ExpressionCompiler

    - #### explain

          public void explain(ExpressionPresenter out)

      Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
      Overrides:
        `explain` in class `UnaryExpression`
      Parameters:
        `out` - the expression presenter used to display the structure

    - #### toString

          public String toString()

      The toString() method for an expression attempts to give a representation of the expression in an XPath-like form. For subclasses of Expression that represent XPath expressions, the result should always be a string that parses as an XPath 3.0 expression.
      Overrides:
        `toString` in class `UnaryExpression`
      Returns:
        a representation of the expression as a string

    - #### getExpressionName

          public String getExpressionName()

      Get a name identifying the kind of expression, in terms meaningful to a user.
      Overrides:
        `getExpressionName` in class `Expression`
      Returns:
        a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in explain() output displaying the expression.

Copyright (c) 2004-2013 Saxonica Limited. All rights reserved.